1) Field of the Invention
The present invention relates to log transport systems and, more particularly, relates to a system and method for transporting logs in a direction of motion while preventing appreciable unwanted motion, such as in directions transverse to the direction of motion, to thereby facilitate processing of the logs, such as by scanning, cutting, and the like.
2) Description of Related Art
During the processing of tree logs, long sections of logs are often transported for a variety of processing steps. For example, according to one conventional process, tree length logs, or xe2x80x9cstems,xe2x80x9d are transported lineally on a motor-driven chain or belt drive mechanism supported by tracks formed of track sections that are welded or bolted together. The logs are passed by or through a scanning device, such as an optical scanner, that detects the size and shape of the log. This information is sent to an optimizing device that determines how each log should be cut, or xe2x80x9cbucked,xe2x80x9d to best yield useful lumber. The logs are then transported by the drive mechanism to a saw that cuts the logs accordingly, for example, by transporting the log against a mechanical stop that hold the log in place and moving the saw transversely to cut the log.
Each log is typically non-uniform along its length, i.e., the log varies in cross-sectional size or shape or defines curves or other non-uniformities. As a result, the belt and chain drive mechanisms may not support the logs evenly, and the logs may therefore move relative to the mechanism in a rocking, bouncing, or sliding motion. Additionally, conventional systems can introduce a certain amount of unwanted motion while transporting the logs, for example, if the track sections are not uniform or not aligned correctly or if the drive mechanism does not move at a uniform speed. The unwanted motion of the logs can adversely affect the accuracy of the scanning or other processing, resulting in sub-optimal processing of the logs.
One prior art method of transporting the logs while reducing unwanted motion is to support the logs on two parallel chains, which can be connected by cross members. The chains are then driven separately or together by motors to lineally transport the logs. This dual-chain system provides better support for the logs, but the chains typically wear and stretch at different rates. If the chains are driven by a single motor, the uneven stretching and wearing can increase the stress on the chains and cross members and decrease the performance of the system. If the chains are driven by separate drive mechanisms, the uneven wearing and stretching of the chains can result in different speeds of the chains, thus imparting additional, nonlinear motion to the logs, adversely affecting other processes such as scanning.
According to another prior art transporting system, the logs are supported by holders spaced incrementally along the length of a single chain. The holders and chain are supported by a track formed of welded or bolted track sections. Each holder defines a stepped slot parallel to the chain for receiving the log. Each stepped slot defines a pair of steps or terraces that extend upwardly in a divergent manner. Logs of different diameters can be received by the slot and supported by the steps. Undesirably, however, the holders may not prevent the logs from sliding in a direction parallel to the chain, for example, while the chain is being started or stopped. Also, even if the holders move at a constant speed, nonuniformities in the track can cause unwanted motion, as described above.
Thus, there exists a need for a log transport system that supports the logs for lineal transport and substantially prevents rocking, bouncing, and sliding of the logs. The system should be capable of transporting logs of various lengths, cross-sectional sizes, and shapes, including logs that are non-uniform along their length. The system should also be compatible with other processes so that the log can be transported for scanning, cutting, and the like.
In accordance with one aspect, the present invention satisfies these and other needs by providing a log transport system, log-carrying lugs therefor, and an associated method of transporting logs. In accordance with one aspect of the present invention, the system includes track(s) that are machined and connected to a frame, and key features keep the frame and track(s) in close alignment to provide substantially continuous and uniform track surfaces. Preferably, lugs with support surfaces that correspond to the track surfaces are configured to support the logs as the lugs are slid longitudinally along the tracks. Thus, the system transports the logs without substantial unwanted transverse motion.
According to one embodiment, the present invention provides a system for transporting a log, including first and second parallel tracks that extend longitudinally. Each of the tracks is formed of track portions, or sections, arranged collinearly to define first and second track surfaces respectively. The first track surface is machined to have a nonlinear cross section, and the second track has a linear surface that extends transversely, or perpendicular to the longitudinal direction of the tracks. The tracks are supported by a frame, and each of the first track portions and the frame define key features, such as keyways that receive keys, for positioning the first track portions relative to the frame so that the first track portions are substantially collinear and the first track surface is uniform and continuous in the longitudinal direction of the track to reduce transverse motion of the log during transport. The key features can extend across interfaces between collinear adjacent portions of the frame to maintain the successive frame portions in alignment.
In accordance with one aspect of the present invention, a plurality of lugs are adapted for supporting the log, each lug extending between the first and second tracks and defining first and second support surfaces that correspond in shape to the first and second track surfaces. For example, the support surfaces can be machined to correspond to the respective track surfaces so that the lugs slide longitudinally along the tracks. The lugs are preferably connected by a plurality of chain links, and configured to be slid along the tracks by a drive device, thereby transporting the log. Replaceable wear strips formed of a low friction material can be disposed between the support surfaces and the track surfaces. The system can also include a scanning device for determining dimensions of the log and a cutting device for transversely cutting the log.
The key features can include a plurality of projections that extend from the frame or track portions and corresponding cavities defined by the other of the frame or track portions. The projections and corresponding cavities can each be prismatically shaped. For example, each projection can be a rectangular prism, which defines four upright perpendicular surfaces that correspond to a respective rectangular cavity and restrict the track portion from moving horizontally in both the longitudinal direction and a lateral direction perpendicular to the longitudinal direction. The key features, for example, the projections and cavities, can be arranged to coincide with interfaces between adjacent track portions so that the ends of the track portions are kept in alignment. Additionally, the track portions can be arranged to overlap interfaces between portions of the frame so that the interfaces between adjacent track portions do not coincide with interfaces between the frame portions. Further, the cavities can extend only partially into the frame or track so that the projection does not extend through the frame and track and the key feature is encapsulated within the combination of the frame and track.
In accordance with one aspect, the present invention also provides a lug for transporting a log. The lug includes opposite first and second portions defining first and second lower surfaces respectively for engaging first and second tracks. The first and second portions also define upper first and second edges opposite the first and second surfaces, which are configured to engage the log (or which may be equipped with spikes for engaging the log). A connection portion extends between the first and second portions and is configured to engage a drive device (e.g., teeth of a motor-driven sprocket). The connection portion can define at least part of a link of a chain so that a plurality of the lugs can be connected/incorporated into an endless conveyor chain. The first and second edges preferably define an angled space therebetween for receiving the log.
According to one aspect of the invention, the lower first and/or second surfaces of the lugs define a contour (e.g., a ridge and/or groove) that corresponds to a track contour (e.g., a ridge and/or groove) extending along the respective track so that the respective lower surface of the lugs can be engaged to the respective track to substantially prevent the lug from being pivoted or translated transversely. For example, one of the surfaces of the lug can define a v-shaped slot that receives/mates with a v-shaped contour of the respective track. The mating surfaces can be at least partially defined by a wear strip that is removable and replaceable.
One aspect of the present invention is the provision of methods of constructing a log transport system, and one exemplary method is described in this paragraph. The method includes providing a plurality of frame portions that define a plurality of key features, machining a plurality of first track portions to define a first track surface and at least one key feature, the first track surface preferably having a nonlinear cross section that is uniform in a longitudinal direction of each track portion, and machining a plurality of second track portions to define a second track surface. A plurality of lugs are formed for supporting the log, each lug defining lower first and second support surfaces corresponding in shape to the respective track surfaces. For example, the first track surface can be machined to define a v-shaped contour, and the lugs can be machined so that one of the support surfaces corresponds thereto. Knife edges or spikes can be provided on upper portions of the lugs to engage the log and substantially prevent the log from moving relative to the lugs. The frame portions are positioned to define a frame extending in a longitudinal direction and having a frame surface. The key features of the first track portions are engaged to the key features of the frame portions so that the track portions define a first track, the first track extending longitudinally and preferably being substantially straight and uniform in shape in the longitudinal direction. For example, the key features can include slots formed in the frame portions and the first track portions, the slots of the frame portions can be respectively adjacent slots of the first track portions, and keys (e.g., blocks) can be respectively inserted into the adjacent slots to engage the first track portions to the frame portions. Key features can also be provided at adjacent ends of the frame portions, and the key features at interfaces of the adjacent ends can be aligned and overlapped with the first track portions. The second track portions are connected to the frame so that the second track portions define a second track extending parallel to the first track. The lugs are configured to extend between the first and second tracks so that the lower support surfaces of the lugs respectively engage the track surfaces. The lugs are also connected to a drive device that is configured to slide the lugs along the tracks in the longitudinal direction. According to one aspect of the invention, replaceable wear strips formed of a low friction material are disposed between the support surfaces of the lugs and the track surfaces. Scanning and/or cutting devices can be provided for determining dimensions of the log and transversely cutting the log.